Carbon fibers are used to make composite materials. Such carbon composites provide the advantages of relatively high strength and low weight as compared to other materials commonly used to form articles such as automotive, boat, airplane and other parts. High strength and low weight are key advantages needed to reduce vehicle fuel consumption and increase fuel economy. The strength of the composite is directly related to the quality of the carbon fibers. Preferred fibers have basal planes arranged in concentric circles and are of microscopic size for improved strength-to-weight ratio. Such microscopic fibers effectively achieve the advantages of improved strength, low weight and, therefore, improved fuel economy.
Prior methods of forming fibers basically consist of conducting a gas phase batch reaction in a vessel. Specifically such methods include dispensing iron particles, in the form of a powder or in a solution, into a vessel while simultaneously dispensing a liquid or gas hydrocarbon compound, then decomposing the hydrocarbon compound to form carbon-containing compounds which react with the iron particles. A diluent gas, such as hydrogen, is injected into the vessel to control the rate at which decomposition and growth proceed.
Prior methods and vessels typically include a preconditioning period and a post-formation period. During the preconditioning period, the surface of the vessel is prepared using iron particles and/or the vessel is preheated before the reaction is initiated. During the post-formation period, the vessel is disassembled to remove fibers and unreacted compounds. The effort required for preparation, and particularly for post-formation, is typically extensive in relation to the amount of product produced. Such methods are not cost effective for use in commercial scale plants.
Therefore, it would be desirable to have an apparatus and method which form carbon fibers in a generally continuous process and which provide a consistently high yield of fibers of desired dimensions.